Back to EveryPatent.com
| United States Patent |
5,780,200
|
|
Kitaguchi
, et al.
|
July 14, 1998
|
Printing plate materials and method of producing the same
Abstract
A printing plate material producing concave-convex pattern on the surface
with a low laser energy output and having high scratch resistance is
provided by formation of a photosensitive layer comprising a
nitrocellulose, carbon black or other photoabsorber and a polyurethane
elastomer on a support. The nitrocellulose has a nitrogen content of about
11 to 12.5% and a solution viscosity of about 1 to 1/8 second. The
polyurethane elastomer is obtainable by allowing a polyester polyol to
react with a polyisocyanate and a chain-extending agent. Relative to 100
parts by weight of the polyurethane elastomer, the amount of
nitrocellulose is about 5 to 300 parts by weight and that of the
photoabsorber is about 0.5 to 50 parts by weight. The photosensitive layer
may have a glass transition temperature of not lower than 25.degree. C.
The photosensitive layer may further comprise a plasticizer.
| Inventors:
|
Kitaguchi; Tohru (Himeji, JP);
Notsu; Kazuo (Amagasaki, JP);
Takahashi; Kazushi (Himeji, JP);
Furukawa; Masayoshi (Himeji, JP);
Kambara; Shigeki (Himeji, JP);
Majima; Osamu (Tokyo, JP);
Kuwahara; Soichi (Tokyo, JP)
|
| Assignee:
|
Daicel Chemical Industries, Ltd. (Osaka, JP)
|
| Appl. No.:
|
564184 |
| Filed:
|
December 18, 1995 |
| PCT Filed:
|
April 19, 1995
|
| PCT NO:
|
PCT/JP95/00764
|
| 371 Date:
|
December 18, 1995
|
| 102(e) Date:
|
December 18, 1995
|
| PCT PUB.NO.:
|
WO95/28288 |
| PCT PUB. Date:
|
October 26, 1995 |
Foreign Application Priority Data
| Apr 19, 1994[JP] | 6-080033 |
| Aug 01, 1994[JP] | 6-180337 |
| Current U.S. Class: |
430/270.1; 430/300; 430/322; 430/945 |
| Intern'l Class: |
G03C 001/73 |
| Field of Search: |
430/300,302,270.1,284.1,322,906,945
522/2
|
References Cited
U.S. Patent Documents
| 5156938 | Oct., 1992 | Foley et al. | 430/200.
|
| 5262275 | Nov., 1993 | Fan | 430/273.
|
| 5330876 | Jul., 1994 | Kaszczuk et al. | 430/269.
|
| Foreign Patent Documents |
| 51-6569 | Feb., 1976 | JP.
| |
| 51-35144 | Sep., 1976 | JP.
| |
| 57-37046 | Aug., 1982 | JP.
| |
| 62-52720 | Nov., 1987 | JP.
| |
| 4-506709 | Nov., 1992 | JP.
| |
| 5-8367 | Jan., 1993 | JP.
| |
| 5-246165 | Sep., 1993 | JP.
| |
| 7-32757 | Feb., 1995 | JP.
| |
| WO90/12342 | Oct., 1990 | WO.
| |
Primary Examiner: Baxter; Janet C.
Assistant Examiner: Ashton; Rosemary
Attorney, Agent or Firm: Birch, Stewart, Kolasch & Birch, LLP
Claims
We claim:
1. A printing plate material which comprises a photosensitive layer
containing a nitrocellulose, a photoabsorber and a polyurethane elastomer
having an elongation percentage of not less than 400% and a glass
transition temperature of not higher than -10.degree. C., and a support on
which said photosensitive layer is formed.
2. The printing plate material as claimed in claim 1, wherein said
nitrocellulose has a nitrogen content of 10 to 14%.
3. The printing plate material as claimed in claim 1, wherein said
nitrocellulose has a degree of polymerization in the range of 10 to 1,500.
4. The printing plate material as claimed in claim 1, wherein said
nitrocellulose has a solution viscosity, according to Japanese Industrial
Standards (JIS) K6703, of 20 to 1/10 second.
5. The printing plate material as claimed in claim 1, wherein said
nitrocellulose has a nitrogen content of 11 to 12.5%, a degree of
polymerization in the range of 10 to 900 and a solution viscosity,
according to JIS K6703, of 10 to 1/8 second.
6. The printing plate material as claimed in claim 1, wherein said
photoabsorber is carbon black.
7. The printing plate material as claimed in claim 1, wherein said
polyurethane elastomer is an elastomer obtainable by allowing a polyester
polyol to react with a polyisocyanate and a chain-extending agent, and has
an elongation percentage of not less than 400% and a glass transition
temperature of not higher than -10.degree. C.
8. The printing plate material as claimed in claim 1, wherein said
polyurethane elastomer has an elongation percentage of 400 to 1,000%, and
a glass transition temperature in the range of -10.degree. C. through
-50.degree. C.
9. The printing plate material as claimed in claim 1, wherein said
photosensitive layer has a glass transition temperature in the range of
-25.degree. C. to 40.degree. C.
10. The printing plate material as claimed in claim 1, wherein said
photosensitive layer has a glass transition temperature of not lower than
25.degree. C.
11. The printing plate material as claimed in claim 1, wherein said
photosensitive layer comprises 5 to 300 parts by weight of the
nitrocellulose and 0.5 to 50 parts by weight of the photoabsorber relative
to 100 parts by weight of said polyurethane elastomer.
12. The printing plate material as claimed in claim 1, wherein said
photosensitive layer comprises 20 to 250 parts by weight of a
nitrocellulose having a nitrogen content of 11.5 to 12.2% and a solution
viscosity, according to JIS K6703, of 1 to 1/8 second, and 2.5 to 40 parts
by weight of carbon black relative to 100 parts by weight of the
polyurethane elastomer.
13. The printing plate material as claimed in claim 1, wherein said
photosensitive layer comprises 50 to 200 parts by weight of the
nitrocellulose and 5 to 50 parts by weight of the photoabsorber relative
to 100 parts by weight of a polyurethane elastomer having an elongation
percentage of 500 to 900% and a glass transition temperature in the range
of -15.degree. C. through -45.degree. C.
14. The printing plate material as claimed in claim 1, wherein said
photosensitive layer further contains a plasticizer.
15. The printing plate material as claimed in claim 14, wherein said
plasticizer is at least one member selected from the group consisting of
camphor, phthalic acid esters, phosphoric esters, adipic acid esters and
sebacic acid esters.
16. The printing plate material as claimed in claim 14, wherein the
proportion of said plasticizer is 0.1 to 30 parts by weight relative to
100 parts by weight of the total amount of said constitutive
nitrocellulose, photoabsorber and polyurethane elastomer in said
photosensitive layer.
17. The printing plate material as claimed in claim 14, which has a
photosensitive layer comprising a nitrocellulose, a photoabsorber and a
polyurethane elastomer and having a glass transition temperature in the
range of 0.degree. C. to 40.degree. C., where the plasticizer is
incorporated into said photosensitive layer in a proportion of 1 to 20
parts by weight relative to 100 parts by weight of the total amount of
said constituting nitrocellulose, photoabsorber and polyurethane elastomer
in said photosensitive layer.
18. A printing photosensitive composition which comprises a nitrocellulose,
a photoabsorber and a polyurethane elastomer having an elongation
percentage of not less than 400% and a glass transition temperature of not
higher than -10.degree. C., and on which a pit may be formed by laser
irradiation.
19. A method of producing a printing plate material which comprises coating
a coating composition comprising a nitrocellulose, a photoabsorber and a
polyurethane elastomer having an elongation percentage of not less than
400% and a glass transition temperature of not higher than -10.degree. C.
on a support to provide a photosensitive layer which can be sculptured
with laser light.
20. The method of producing a printing plate material according to claim
19, wherein said coating composition further comprises a plasticizer and
is coated on said support.
Description
TECHNICAL FIELD
This invention relates to a printing plate material which can be sculptured
with laser light and to a method for its production.
BACKGROUND TECHNOLOGY
A laser-sculptured printing plate material is known which comprises a
mixture of polyethylene and carbon black as molded in the form of a sheet.
However, this material requires high-energy laser radiation for creating a
concave-convex (three-dimensional) pattern on its surface. For this
reason, any printing plate material on which a three-dimensional pattern
can be produced with a low-energy laser radiation has not been
commercially implemented yet.
Meanwhile, a recording material supplemented with nitrocellulose for
enhanced sensitivity is known but this material is deficient in the
strength required of any printing plate. By way of example, Japanese
Patent Publication No. 35144/1976 (JP-B-51-35144) discloses an image
forming technology which comprises coating a support with a photosensitive
composition containing nitrocellulose and carbon black and irradiating the
coated support with laser light from behind the support which is coated
with a photosensitive layer to form an image. Described in this prior art
literature is an embodiment in which an ink is transferred to the
photosensitive layer for printing. However, this photosensitive layer is
invariably of low film strength so that the final material is not
practically useful as a printing plate.
Japanese Patent Publication No. 6569/1976 (JP-B-51-6569) discloses an
image-forming printing plate material having a photosensitive layer
containing nitrocellulose as a self-oxidative binder, carbon black as a
particulate pigment capable of absorbing laser energy, and melamine resin
as a curing agent (cross-linking agent). This literature describes
examples in which an alkyd resin, a methyl methacrylate resin, a butyral
resin, an epoxy resin or a novolac resin is further used as a binder
resin. However, the photosensitive material described in the above
literature is designed for use in the process for producing a lithographic
or planographic printing plate which comprises contacting the
photosensitive coating layer coated on a support with the polyvinyl
alcohol coating layer coated on an aluminum plate and irradiating them
with laser light from behind the support to thereby transfer an image
corresponding to the irradiated area to the aluminum plate. Therefore, it
is not a printing plate belonging to the category in which a printing ink
is directly transferred on a photosensitive layer for printing. Moreover,
the film strength of the photosensitive layer formed with the
photosensitive material is not sufficiently high so that the product can
hardly be used, as it is, as a printing plate.
Japanese Patent Application Laid-open No. 506709/1992 (JP-A-4-506709)
corresponding to W090/12342 discloses an imaging material as produced
using a composition comprising a sensitizer which is capable of absorbing
an infrared ray, and a polyurethane as a decomposable binder. The material
described in this literature is, however, belonging to the category of a
thermal transferring color imaging material where a reverse image is
formed by partial thermal decomposition of the decomposable binder and
thus transferring the remained binder and a pigment to a receptor sheet.
Therefore, it is not a printing plate belonging to the category in which a
printing ink is directly transferred on a photosensitive layer for
printing.
Accordingly, it is an object of the present invention to provide a printing
plate material which can be sculptured even at a low laser energy output,
and which can be used in a printing process comprising transferring a
printing ink directly on the surface of its layer having a concave-convex
(three-dimensional) pattern produced with laser light and has excellent
durability and wear resistance (printing pressure resistance) in
association with printing, and a method of producing the printing plate
material.
It is another object of the present invention to provide a printing plate
material which comprises a photosensitive layer having a high sensitivity
(thermodegradability) relative to laser light, and insuring excellent
scratch resistance (scar resistance) and blocking resistance in spite of
containing an elastomer, and a method of producing the same.
A further object of the present invention is to provide a printing plate
material provided with a photosensitive layer which insures an improved
sensitivity relative to laser light while maintaining its high scratch
resistance and blocking resistance, and a method of producing such
printing plate material.
It is still another object of the present invention to provide a
composition which is useful to form a photosensitive layer having such
excellent characteristics as mentioned above.
A yet another object of the present invention is to provide a method of
printing in which blocking of a photosensitive layer in storage process
can be inhibited and rubber elasticity can effectively be exhibited in
printing process.
DISCLOSURE OF THE INVENTION
The inventors of the present invention did intensive research to accomplish
the above-mentioned objects and found that by forming a photosensitive
layer comprising a nitrocellulose, a photoabsorber, and a polyurethane
elastomer as a binder resin on a support, a printing material having a
photosensitive layer which is highly thermodegradable on exposure to laser
radiation and has a high film strength and scratch resistance can be
obtained. The present invention has been developed on the basis of the
above finding.
Thus, the printing plate material of the present invention comprises a
photosensitive layer comprising a nitrocellulose, a photoabsorber and a
polyurethane elastomer, and a support on which the photosensitive layer is
formed. As the nitrocellulose, a variety of nitrocelluloses which can be
thermally decomposed with laser light, for example a nitrocellulose with a
nitrogen content of about 10 to 14%, a degree of polymerization in the
range of about 10 to 1,500, and a solution viscosity, according to
Japanese Industrial Standards (JIS) K6703, of about 20 to 1/10 second. The
photoabsorber includes carbon black or others, and the polyurethane
elastomer includes, for example, a polyurethane elastomer having an
elongation percentage of not less than 400% and a glass transition
temperature of not higher than -10.degree. C. The photosensitive layer of
the printing plate material may contain a plasticizer.
The above printing plate material may be manufactured by coating a support
such as a film with a coating composition comprising a nitrocellulose, a
photoabsorber, a polyurethane elastomer, and if necessary, a plasticizer
to provide a photosensitive layer which can be sculptured with an
application of laser light.
As used throughout this specification, the term "film" includes a sheet
unless otherwise specified.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a graph illustrating a relationship between a nitrocellulose
content in a photosensitive layer, and a glossiness retention in
association with abrasion or wearing and a glass transition temperature of
the photosensitive layer.
DETAILED DESCRIPTION OF THE INVENTION
The printing plate material of the present invention comprises a
photosensitive layer comprising a nitrocellulose, a photoabsorber and a
polyurethane elastomer, and a support. The species of the nitrocellulose
to be incorporated in the photosensitive layer is not particularly
restricted only if it is thermally degradable, and may be whichever grade
of RS (regular soluble) type or grade, SS (spirit soluble) type and AS
(alcohol soluble) type. The nitrogen content of the nitrocellulose is
generally about 10 to 14%, preferably about 11 to 12.5%, and more
preferably about 11.5 to 12.2%. The degree of polymerization of the
nitrocellulose can also liberally be selected within a broad range of, for
example, about 10 to 1,500. The preferred degree of polymerization of the
nitrocellulose may, for instance, be about 10 to 900 and particularly
about 15 to 150. The preferred nitrocellulose includes a nitrocellulose
with a solution viscosity of about 20 to 1/10 second, preferably about 10
to 1/8 second, as determined in accordance with Japanese Industrial
Standards (JIS) K6703 "Industrial Nitrocellulose" (the viscosity
denomination of Hercules Powder Company). The practically used
nitrocellulose has a solution viscosity of about 5 to 1/8 second,
particularly about 1 to 1/8 second. If necessary, two or more species of
nitrocellulose can be used in combination.
The amount of the nitrocellulose may be selected from a range not adversely
affecting the sensitivity of the photosensitive layer and may be about 5
to 300 parts by weight, preferably about 20 to 250 parts by weight, and
more preferably about 50 to 200 parts by weight relative to 100 parts by
weight of the polyurethane elastomer. The nitrocellulose may practically
be used in a proportion of about 40 to 200 parts by weight relative to 100
parts by weight of the polyurethane elastomer.
The photoabsorber (photoabsorbing component) includes a variety of
absorbers which absorb laser energy with high efficiency, such as a black
dye and other dyes and carbon material. The preferred species of the
carbon material includes carbon black, and insofar as a high dispersion
stability can be imparted to the composition, any of the species defined
in American Society for Testing Materials (ASTM) and/or indicated for
whatever uses (e.g. colors, rubber, dry batteries, etc.) can be employed.
For example, the carbon black includes furnace black, thermal black,
channel black, lamp black and acetylene black and the like.
A black coloring agent such as carbon black can be used in the form of
color chips or a color paste, which can be prepared by dispersing it
beforehand in a nitrocellulose, and when necessary using a dispersing
agent, in which case the dispersion thereof is facilitated. Such chips and
paste are readily available from commercial sources.
The amount of the photoabsorber may be selected from the range not
sacrificing the sensitivity of the photosensitive layer and is, for
example, about 0.5 to 50 parts by weight, preferably about 2.5 to 40 parts
by weight and more preferably about 10 to 30 parts by weight relative to
100 parts by weight of the polyurethane elastomer. The photoabsorber may
practically be employed in a proportion of about 5 to 50 parts by weight
relative to 100 parts by weight of the polyurethane elastomer.
A feature of the present invention, in one aspect, resides in a combination
use of the nitrocellulose and the photoabsorber with a polyurethane
elastomer. The above photosensitive layer of the printing plate material
has such advantages that a pit pattern (three-dimensional pattern) can be
formed on the photosensitive layer even at a low laser energy output and
the film strength and scratch resistance of the photosensitive layer can
be enhanced. Further, a high scratch resistance, and thus a high
durability and printing press resistance can be expected even when a
printing ink is directly transferred to the three-dimensionally patterned
photosensitive layer.
The species of the polyurethane elastomer may not be particularly
restricted insofar as not interfering with the sensitivity to laser light,
printing press resistance or other properties of the photosensitive layer.
As such polyurethane elastomer, there may be used a variety of
polyurethane elastomers which are obtainable by using a polyol such as a
polyester polyol, a polyether polyol and an acrylpolyol, a polyisocyanate,
and as necessary, a chain-extending agent or chain-extending component
such as a polyhydric alcohol and/or a polyamine. The polyol may be used
singly or in combination, and it may practically comprise at least a
polyester polyol. As the polyester polyol, a linear polyester polyol can
preferably be for its high elasticity, but a polyester polyol having a few
branches may also be employed because the viscosity increases with an
increasing molecular weight.
The components of the polyester polyol include a polycarboxylic acid
component and a polyhydric alcohol component. The polycarboxylic acid
component includes, for instance, aromatic carboxylic acids such as
phthalic acid, isophthalic acid, terephthalic acid, etc. or the
corresponding anhydrides; saturated or unsaturated aliphatic carboxylic
acids such as glutaric acid, adipic acid, azelaic acid, sebacic acid,
maleic acid, fumaric acid, dimeric linolenic acid and the like, or the
corresponding anhydrides. These polycarboxylic acid components may be used
independently or in combination. As such aliphatic carboxylic acid,
saturated aliphatic dicarboxylic acids such as adipic acid, azelaic acid,
sebacic acid and so on may practically be employed.
As examples of the polyhydric alcohol component, there may be mentioned
aliphatic dihydric alcohols such as ethylene glycol, propylene glycol,
trimethylene glycol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, etc.; polyoxyalkylene
glycols such as diethylene glycol, triethylene glycol, tetraethylene
glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol and
so forth; aliphatic polyhydric alcohols such as glycerin,
trimethylolpropane, trimethylolethane, hexanetriol, pentaerythritol, etc.;
and bisphenol A-alkylene oxide adducts such as
2,2-bis(4-dihydroxypropylphenyl)propane, typically speaking. These
polyhydric alcohol components can also be employed singly or in
combination. As the polyhydric alcohol component, at least an aliphatic
dihydric alcohol and/or a polyoxyalkylene glycol may generally be used.
The molecular weight of the polyester polyol may for example be about 500
to 5,000, preferably about 700 to 3,000, and more preferably about 1,000
to 2,000.
Examples of the polyisocyanate include aromatic diisocyanates such as
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, phenylene
diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate,
1,5-naphthalene diisocyanate and the like; aliphatic diisocyanates such as
1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate,
1,10-decamethylene diisocyanate and so forth; and alicyclic diisocyanates
such as isophorone diisocyanate and so on. Such polyisocyanates can be
employed singly or in combination.
As the chain-extending agent (chain-extender), use may be made of
polyhydric alcohols as exemplified above (e.g. diols (dihydric alcohols)
such as ethylene glycol, propylene glycol, trimethylene glycol,
1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol,
1,6-hexanediol and neopentyl glycol, polyols (polyhydric alcohols) such as
glycerin, trimethylolpropane, trimethylolethane, pentaerythritol and so
on). By the same token, polyamines can also be used as the chain-extending
agent. Examples of such polyamide include (poly)alkylenepolyamines such as
ethylenediamine, diethylenetriamine, triethylenetetramine,
hexamethylenediamine, propylenediamine, etc.; and alkanolamines such as
monoethanolamine, diethanolamine, triethanolamine and so forth. Polyhydric
alcohols can preferably be used as the chain-extending agent.
The polyurethane elastomer may practically be prepared by a reaction of a
polyester polyol, polyisocyanate and a polyhydric alcohol, or a reaction
of a prepolymer having an isocyanate group with a chain-extending agent
(e.g. polyhydric alcohols, etc.). Such prepolymer is produced by allowing
a polyol such as the above-mentioned polyester polyol to react with a
polyisocyanate.
As the polyurethane elastomer, whichever of elastomers may be used as far
as not adversely affecting the sensitivity to laser light, strength or
other properties of the photosensitive layer. Preferred example of the
polyurethane elastomer includes a polyurethane elastomer having an
elongation percentage (extension percentage) of not less than 400% (e.g.
about 400 to 1,000%), preferably not less than 500% (e.g. about 500 to
900%). The glass transition temperature (Tg) of the polyurethane elastomer
may for example be not higher than -10.degree. C. (e.g. about -10.degree.
C. through -50.degree. C.), preferably not higher than -15.degree. C.
(e.g. about -15.degree. C. through -45.degree. C.) and more preferably not
higher than -20.degree. C. (e.g. about -20.degree. C. through -40.degree.
C.).
The glass transition temperature of the photosensitive layer may for
example be about -25.degree. C. to 40.degree. C., preferably about
-15.degree. C. to 35.degree. C., and more preferably about -10.degree. C.
to 30.degree. C. While, depending on the proportion of the nitrocellulose
relative to the polyurethane elastomer, blocking of the photosensitive
layer may occasionally occur when sheet-like printing plate materials are
piled up. Accordingly, in order to improve the durability and scratch
resistance of the material with inhibiting or suppressing such blocking of
the photosensitive layer, the glass transition temperature of the
photosensitive layer may preferably be not lower than 25.degree. C. (e.g.
about 25.degree. C. to 40.degree. C.), and preferably about 25.degree. C.
to 35.degree. C.
In more detail, the glass transition temperature of a polyurethane
elastomer is, usually, lower than room temperature, and is about
-15.degree. C. through -50.degree. C., typically speaking. When a
photosensitive layer is formed using such polyurethane elastomer and a
nitrocellulose, the glass transition temperature of the photosensitive
layer increases or elevates with an increasing proportion of the
nitrocellulose, because the nitrocellulose has a high glass transition
temperature. By way of illustration as shown in FIG. 1, the glass
transition temperature of a film elevates with an increasing amount of the
nitrocellulose, in a photosensitive layer formed with a composition
comprising a polyurethane elastomer with a glass transition temperature of
-23.degree. C., a nitrocellulose with a glass transition temperature of
about 60.degree. C. and 10% by weight of carbon black. In fact, for the
film which contains 33.7% by weight of the nitrocellulose, the glass
transition temperature of the film is about -10.degree. C., and hence it
exhibits rubber elasticity at room temperature. While, the degree of wear
or abrasion caused by an abrasion wheel decreases with an increasing
nitrocellulose content. That is, when the scratch resistance (flaw
resistance) is evaluated by a glossiness retention as determined by
altering the abrasion times (repetition times of wearing process) with the
glossiness of a non-abraded sample being 100%, as illustrated in FIG. 1,
the flaw resistance decreases with an increasing nitrocellulose content in
the photosensitive layer, and is in an approximately fixed level when the
nitrocellulose content is about 40% by weight or more. This is provably
because the glass transition temperature becomes about 30.degree. C. or
higher in a case with a nitrocellulose content of not less than 40% by
weight so that the rubber elasticity will not exhibit at room temperature
(around 25.degree. C.).
As described above, when a photosensitive layer has rubber elasticity at
room temperature, and a printing plate material provided with such
photosensitive layer is piled up with other sheet or film with a load
weighed thereon, there possibly occurs blocking phenomenon where the
photosensitive layer and the sheet or film are adhered or stuck to each
other. Accordingly, by controlling the glass transition temperature of a
photosensitive layer to be not lower than 25.degree. C. (e.g. 25.degree.
C. to 40.degree. C.), the photosensitive layer is almost in a glassy state
at room temperature so that such risk of the blocking of material can be
unburdened. A printing plate material having a photosensitive layer with
such glass transition temperature has the following advantages. Namely,
when the printing plate material is stored at room temperature or lower,
blocking of the photosensitive layer with a sheet or others can be
inhibited. On the other hand, when the material is used as a plate
material in a printing process where a pit pattern is formed on exposure
to laser light and a flaw resistance of the material is required, the
photosensitive layer can exhibit the rubber elasticity by printing at a
temperature higher than the glass transition temperature of the
photosensitive layer so that scratch formation of the photosensitive layer
during the printing process can be prevented.
The glass transition temperature of the photosensitive layer can be
adjusted or controlled according to the relative proportion of the
nitrocellulose to the polyurethane elastomer, as described above.
According to differential scanning thermal analysis, a photosensitive
layer comprising a nitrocellulose and a polyurethane elastomer generally
shows a single peak which is not found in the nitrocellulose and
polyurethane elastomer as such, while such peak depends on the species of
the constituting components and photosensitive layer. Therefore, it is
supposed that the nitrocellulose and polyurethane elastomer are compatible
with each other in the photosensitive layer.
In such photosensitive layer, a high nitrocellulose content for an improved
sensitivity to laser light and thereby a high glass transition temperature
may occasionally result in decreased scratch resistance and durability. In
such a case, addition of a plasticizer is useful. That is, even when the
nitrocellulose content is increased, addition of a plasticizer results in
an inhibition of increase of the glass transition temperature of the
photosensitive layer and hence insures high durability and scratch
resistance (wear resistance). Further, the sensitivity (thermal
degradability) to laser light can also be improved with an increasing
amount of the nitrocellulose. The plasticizer may effectively be
incorporated into a composition which constitutes a photosensitive layer
with a glass transition temperature of about 0.degree. C. through
40.degree. C., preferably about 10.degree. C. through 30.degree. C.
As the species of plasticizer, there is no particular restriction and
whichever plasticizer can be employed as far as thereby a photosensitive
layer comprising a nitrocellulose, a photoabsorber and a polyurethane
elastomer is plasticizable. The plasticizer includes, for instance,
camphor or its derivative, phthalic acid esters (e.g. dimethyl phthalate,
diethyl phthalate, dibutyl phthalate, diisobutyl phthalate, dihexyl
phthalate, dioctyl phthalate di(2-ethylhexyl) phthalate, etc.), phosphoric
esters (e.g. triphenyl phosphate, tricresyl phosphate, etc.), adipic acid
esters (e.g. di(2-ethylhexyl) adipate, etc.), sebacic acid esters (e.g.
dibutyl sebacate, etc.) and so on. These plasticizers may be used
independently or in combination.
The amount of the plasticizer can be selected according to the species of
the nitrocellulose and polyurethane elastomer, the glass transition
temperature of the photosensitive layer and/or other factors, for example
within the range of about 0.1 to 30 parts by weight, preferably about 1 to
20 parts by weight, and more preferably about 2 to 15 parts by weight
relative to 100 parts by weight of the composition for the photosensitive
layer (i.e. the total amount of the nitrocellulose, photoabsorber and
polyurethane elastomer).
If required, the photosensitive layer may contain a variety of additives
such as antioxidants, ultraviolet absorbers or other aging inhibitors,
crosslinking agents, crosslinking accelerators (cure accelerators), flame
retardants, fillers, coloring agents, leveling agents and so on.
The shape of the support is not restricted only if it is printable form and
may for example be drum-like, film-like, sheet-like or other form.
Although the material of the support is not particularly limited, a
poly(ethylene terephthalate) film or other polymer film may practically be
employed when a support of film or sheet form is chosen. Where necessary,
the support may be surface-treated, or an under coating layer (adhesive
layer) may be interposed between the photosensitive layer and the support
for an improved adhesivility (adhesive property) to the photosensitive
layer.
The thickness of the photosensitive layer formed on the support can be
selected within the range not sacrificing the durability or other
properties of the photosensitive layer and is, for instance, about 1 to
100 .mu.m, preferably about 10 to 50 .mu.m, and practically about 15 to 30
.mu.m.
The above-mentioned photosensitive layer may be formed by coating such a
support with a coating composition comprising a nitrocellulose, a
photoabsorber and a polyurethane elastomer. The coating composition may be
prepared by mix-dispersing the nitrocellulose, photoabsorber and
polyurethane elastomer in an organic solvent using a conventional mixer or
dispersing machine. The organic solvent includes, for example, alcohols
such as ethanol, isopropanol and so on; aliphatic hydrocarbons such as
hexane, octane and the like; alicyclic hydrocarbons such as cyclohexane,
etc.; aromatic hydrocarbons such as benzene, toluene, xylene and so forth;
halogenated hydrocarbons such as dichloromethane, dichloroethane, etc.;
ketones such as acetone, methyl ethyl ketone and the like; esters such as
ethyl acetate, butyl acetate and so on; ethers such as diethyl ether,
tetrahydrofuran, etc.; and various mixtures of these solvents.
As the photosensitive layer formed in the above manner is irradiated with
laser light image-wise, i.e. in accordance with a predetermined pattern,
there is obtained a printing plate having a three-dimensional pattern
(pit) in the photosensitive layer. Where the support is transparent, the
laser beam may be projected from the support side to the photosensitive
side, or irradiation may be performed from the photosensitive side. As the
source of laser radiation, there may used various types of lasers such as
Ar lasers, He--Ne lasers, He--Cd lasers, CO.sub.2 lasers, YGA lasers and
semiconductor lasers, typically speaking.
INDUSTRIAL APPLICABILITY
The printing plate material of the present invention can be used as the
printing plate for gravure printing, flexo printing and other printing
applications, as formed with a pit pattern (three-dimensional pattern) by
irradiation of laser light.
EXAMPLES
The following examples are intended to describe this invention in further
detail but should by no means be interpreted as defining the scope of the
invention.
Example 1
A paint shaker preloaded with ceramic beads (3 mm in diameter) was charged
with 7.7 parts by weight of a nitrocellulose RS 1/4 (Daicel Chemical
Industries, Ltd., isopropyl alcohol-wetted, nonvolatile 70% by weight),
21.1 parts by weight of a carbon black paste (Toyo Ink Manufacturing, Co.,
Ltd., Color Paste ANP-C-903 Black, carbon black content of 12% by weight,
nitrocellulose H 1/2 content of 18% by weight), 40.1 parts by weight of a
polyurethane elastomer (Nippon Polyurethane Industries, Ltd., N2304,
nonvolatile 35% by weight, elongation percentage of 750%, glass transition
temperature of -23.degree. C.), and 32.2 parts by weight of methyl ethyl
ketone, and the charged was mixed and dispersed by shaking for 30 minutes
to give a coating composition. Using an applicator, the resulting coating
composition was coated in a dry thickness of 25 .mu.m on a poly(ethylene
terephthalate) film (188 .mu.m in thickness) and dried at 110.degree. C.
for 2 minutes to provide a printing plate material.
Examples 2 to 9
Printing plate materials each having a photosensitive layer with a
composition (formulation) as set forth in Table 1 were obtained in the
same manner as Example 1 except that the proportions of the components in
Example 1 were changed.
Examples 10 and 11
By repeating the procedure of Example 1, printing plate materials each
having a photosensitive layer with a composition shown in Table 1 were
obtained except for using a polyurethane elastomer (Nippon Polyurethane
Industries, Ltd., N3022, nonvolatile 35% by weight, elongation percentage
of 800%, glass transition temperature of -38.degree. C.) in lieu of the
polyurethane elastomer used in Example 1, and employing the
nitrocellulose, carbon black paste and methyl ethyl ketone used in Example
1.
Examples 12 and 13
The procedure of Example 1 was repeated except that a polyurethane
elastomer (Nippon Polyurethane Industries, Ltd., N3107, nonvolatile 40% by
weight, elongation percentage of 850%, glass transition temperature of
-33.degree. C.) was employed in stead of the polyurethane elastomer used
in Example 1, and the nitrocellulose, carbon black paste and methyl ethyl
ketone of Example 1 were used to provide printing plate materials each
having a photosensitive layer with a composition set forth in Table 1.
Examples 14 and 15
By using a polyurethane elastomer (Nippon Polyurethane Industries, Ltd.,
N3118, nonvolatile 40% by weight, elongation percentage of 800%, glass
transition temperature of -38.degree. C.) in lieu of the polyurethane
elastomer used in Example 1 and employing the nitrocellulose, carbon black
paste and methyl ethyl ketone, printing plate materials each having a
photosensitive layer with a composition shown in Table 1 were obtained.
Example 16
A printing plate material having a photosensitive layer with a composition
set forth in Table 1 was manufactured by using a polyurethane elastomer
(Nippon Polyurethane Industries, Ltd., N3110, nonvolatile 25% by weight,
elongation percentage of 700%, glass transition temperature of -15.degree.
C.) in stead of the polyurethane elastomer used in Example 1, and
employing the nitrocellulose, carbon black paste and methyl ethyl ketone
used in Example 1.
Comparative Example 1
A printing plate material was manufactured in the same manner as Example 1
except for employing 7.7 parts by weight of a nitrocellulose RS 1/4
(Daicel Chemical Industries, Ltd., isopropanol-wetted, nonvolatile 70% by
weight), 24.6 parts by weight of a carbon black paste (Toyo Ink
manufacturing, Co., Ltd., Color Paste ANP-C-903 Black), 43.3 parts by
weight of a polyester resin (Toyobo Co., Ltd., Vylon 20SS, nonvolatile 30%
by weight), 5.4 parts by weight of a crosslinking agent (Dainippon Ink and
Chemicals, Inc., melamine resin, Super-Beckamine L-105-60, nonvolatile 60%
by weight), 0.4 part by weight of an acid catalyst (BYK Co., BYK CATALYST
450, nonvolatile approximately 40% by weight) and 18.7 parts by weight of
methyl ethyl ketone.
Comparative Example 2
The procedure of Example 1 was repeated except for using 14.4 parts by
weight of a nitrocellulose RS 1/4 (Daicel Chemical Industries, Ltd.,
isopropanol-wetted, nonvolatile 70% by weight), 3.7 parts by weight of
carbon black (Mitsubishi Chemical Industries Ltd., MA100), 78.1 parts by
weight of a vinyl chloride-vinyl acetate copolymer (Denki Kagaku Kogyo
Co., Ltd., Denka Vinyl 1000C), 10.9 parts by weight of methyl ethyl
ketone, 4.3 parts by weight of isopropanol and 8.6 parts by weight of
toluene to provide a printing plate material.
The printing plate materials obtained in each example and Comparative
Example 1 were abraded with the use of Taber's abrasion apparatus (Yasuda
Seiki Co., Ltd., Taber's abrasion tester, abrading wheel CS-10, load 500
g). The scratch resistance of each abraded printing plate material was
evaluated by determining, with the use of a glossimeter (Moritex Co.,
Ltd., PRANGE Glossimeter RB3, incident angle and reflection angle
=60.degree.), the decrease of glossiness of the material associated with
the repetition of abrading. The glossiness in the predetermined times of
abrasion (20 times, 50 times and 100 times) was determined with the
glossiness of the non-abraded sample being 100%. The results are set forth
in Table 1.
TABLE 1
______________________________________
Composition of photosensitive
layer (weight %)
Carbon Glossiness (%)
Nitrocellulose black Resin 50 times
100 times
______________________________________
Example 1
35.5 10 54.5 61.0 54.8
Example 2
33.75 10 56.25
61.0 54.8
Example 3
35 11.5 53.5 53.7 37.6
Example 4
25 10 65 72.7 68.8
Example 5
35 10 55 52.6 38.2
Example 6
37 5 58 63.2 54.3
Example 7
35 10 55 63.0 52.1
Example 8
33 15 52 59.2 49.4
Example 9
31 20 49 60.5 52.2
Example 10
35.75 10 54.25
83.2 77.9
Example 11
41 10 49 55.6 41.1
Example 12
35.75 10 54.25
76.1 68.3
Example 13
41 10 49 66.4 51.1
Example 14
35.75 10 54.25
78.5 69.3
Example 15
45 10 45 66.8 56.5
Example 16
25 10 65 55.1 40.1
Comp. Ex. 1
38.1 11.5 50.4 30.2 20.2
______________________________________
Besides, the plate material according to Example 1 was fixed on a rotating
drum, rotated at a rate of 3 rps and irradiated with a pulse ray of a
semiconductor laser (He--Cd laser, wave length 441 nm, 5 mW) for 50 msec
to produce pits on the photosensitive layer of the plate material. As a
result, pits having excellent geometry (configuration) with a sharp edge
and a rather smooth (scarce concave-convex) bottom were provided. Further,
the pits had satisfactory depth of 5.86 .mu.m, as determined with the use
of a scanning laser microscope (LASERTEC Co., 1LM21), which demonstrated
high sensitivity of the photosensitive layer to laser light. Therefore,
even at a high speed, a three-dimensional pattern (pit) could be formed by
laser irradiation on such material. On the contrary, when the depth of
pits in the plate material according to Comparative Example 2 was
evaluated by irradiating laser light in the same manner as above, the
depth of pits was shallow and hence it could not precisely be determined
with a laser microscope. Moreover, the pits had a geometry or
configuration with a obscure edge and greatly corrugated bottom.
Example 17
According to the manner of Example 1, a printing plate material was
manufactured except for employing 9.3 parts by weight of a nitrocellulose
RS 1/4 (Daicel Chemical Industries, Ltd., isopropanol-wetted, nonvolatile
70% by weight), 20.8 parts by weight of a carbon black paste (Toyo Ink
Manufacturing, Co., Ltd., Color Paste ANP-C-903 Black, carbon black
content of 12% by weight, nitrocellulose H 1/2 content of 18% by weight),
5 35.0 parts by weight of a polyurethane elastomer (Nippon Polyurethane
Industries, Ltd., N2304, nonvolatile 35% by weight, elongation percentage
of 750%, glass transition temperature of -23.degree. C.) and 34.9 parts by
weight of methyl ethyl ketone.
The glass transition temperature of the photosensitive layer was 26.degree.
C. as determined using a differential scanning calorimeter (DSC).
The resultant glossiness of the photosensitive layer of the material in
association with 100 times-abrasion at temperatures of 23.degree. C. and
50.degree. C. was respectively 26.2% (23.degree. C.) and 50.1% (50.degree.
C.) as determined in the same manner as above. Thus, the scratch
resistance was improved at a temperature higher than the glass transition
temperature of the photosensitive layer.
Further, the photosensitive layer of the plate material was irradiated by
pulse ray of a semiconductor laser light in the above-mentioned manner,
and pits having a satisfactory configuration with a sharp edge and a
rather smooth bottom were obtained. The photosensitive layer showed high
sensitivity with a satisfactory pit depth of 5.86 .mu.m as determined with
a scanning laser microscope (LASERTEC Co., 1LM21).
Furthermore, the obtained plate material was subjected to blocking test in
the following manner. That is, the plate material was cut into 2 pieces
with a square configuration (5 cm.times.5 cm), the 2 pieces were piled up
with the photosensitive layers facing to each other, and the pile of the
plate materials was further put between glass plates having the same areas
with that of the cut materials, and a load of 1 kg was weighed on thus
obtained test piece at 40.degree. C. As a result, blocking was not
observed even after 5 hours from the initial of weighing.
Example 18
A printing plate material was obtained in the similar manner to Example 1
except that 5.1 parts by weight of a nitrocellulose RS 1/4 (Daicel
Chemical Industries, Ltd., isopropanol-wetted, nonvolatile 70% by weight),
22.9 parts by weight of a carbon black paste (Toyo Ink Manufacturing, Co.,
Ltd., Color Paste ANP-C-903 Black LV, carbon black content of 10% by
weight, nitrocellulose H 1/2 content of 15% by weight), 26.4 parts by
weight of a polyurethane elastomer (Nippon Polyurethane Industries, Ltd.,
N2304, nonvolatile 35% by weight, elongation percentage of 750%, glass
transition temperature of -23.degree. C.), 1.4 part by weight of camphor
and 44.3 parts by weight of methyl ethyl ketone were used and the
mix-dispersing was conducted for 1 hour using the paint shaker.
Examples 19 and 20
The procedure of Example 18 was repeated except for changing the
proportions of the components used in Example 18 to give printing plate
materials each having a photosensitive layer with a composition shown in
Table 2.
The glossiness associated with 50 times- and 100 times-abrasion of the
plate materials according to each example was determined. The results are
set forth in Table 2.
TABLE 2
__________________________________________________________________________
Composition of photosensitive layer (weight %)
Glossiness (%)
Nitrocellulose
Carbon black
Resin
Plasticizer
50 times
100 times
__________________________________________________________________________
Example 18
35.1 11.5 46.4
7.02 54.8 40.5
Example 19
35 11.5 47.06
6.44 54.8 40.5
Example 20
40.9 11.5 40 7.61 51.5 38.4
__________________________________________________________________________
Further, the photosensitive layer of each printing plate material was
irradiated, in the same manner as above, by a pulse radiation of a
semiconductor laser light to form pits, and resultantly it showed high
sensitivity to laser light with a pit depth of 6.25 .mu.m. The pits had a
good configuration with a sharp edge and rather smooth bottom.
Top